1. Field of the Invention
The present invention relates to a device to adjust the position of optical len which are movable relative to each other, and particularly to a device to adjust the position of the optics of a zooming mechanism or the like movable along the optical axis.
2. Description of the Prior Art
In case of the zoom lenses for motion picture cameras or the like in which the focusing distance is to be varied continuously, while at the same time the focusing plane is to coincide with the plane of the photosensitive material, there often takes place errors in the position of the focusing plane due to manufacturing errors of the elements or assembly errors. In case these errors exist, the photographs taken are out of focus no matter how exactly the focusing is carried out with the distance measuring mechanism, because the focusing point does not coincide with the film plane in the middle focusing distance during the zooming operation. Until now there was no other way to avoid the focusing error by the zooming operation than to check strictly the manufacturing error of the elements, while as the zooming ratio increases the manufacturing limit has become more limited so that the manufacturing accuracy far beyond the working capacity of the element has come to be desired.
Under such circumstance a method has been adopted, whereby the manufacturing accuracy of the cam grooves to move the zooming lenses are allowed to remain within a certain range, and only one side of the walls of the cam grooves is worked with high accuracy while the other side of the walls of the cam grooves is not worked with as high an accuracy leaving some space between the shaft inserted in the cam grooves and the cam grooves, in such a manner that the cam grooves can be manufactured easily as wide grooves, while the shafts of the zooming lenses are kept always pressed against the side worked with high accuracy of the walls of the cam grooves, when the zooming lenses are moved along such cam grooves.
In such a case, the cam grooves have to be provided inclined to the optical axis of the zooming lenses to be moved in such a manner that at some places the angle of this inclination becomes so large that between the shaft of the zooming lenses and the cam grooves there often takes place components of forces along the direction perpendicular to the optical axis when the shafts of the zooming lenses are pressed by the ordinary spring along only one direction, whereby the components of forces work along the direction to rotate the zooming operation ring so that at the end of the zooming operation, the zooming operation ring and the so called cam ring are rotated a little by the above rotating forces in such a manner that the zooming lenses are moved along the direction of the optical axis or are inclined toward the optical axis, which is very inconvenient.